For some types of fishing it is desirable to maneuver the hook and bait along the bottoms of lakes, rivers and streams. However, particularly if the water is fast moving, the hook can be drawn to the water surface because of its light weight. Thus it is common to provide a weight that is attached to the fishing line a couple of feet back from the hook. The weight sinks below the water surface and carries with it the fishing hook. The term commonly applied to this weight is fish line sinker.
The fish line sinker can have a further function as a weight for casting. Without a weight on the end of the line, the line cannot be easily cast. Thus the fish line sinker is preferably designed so that it is of a shape and size that will contribute to the casting function. Perhaps more appropriately stated, the casting function is considered when designing the fish line sinker.
A problem that occurs with the use of fish line sinkers is that the sinker can sink to the bottom of the stream or lake and get wedged between rocks and the like. When this happens, unless the fisherman is successful is freeing the sinker, the line has to be broken or cut. The bait, hook, sinker and length of fish line are lost, a very annoying experience.